It looks like this story is very nuanced.

In South Australia, there is so much solar power that the wholesale electricity price frequently goes negative. I don't know about Tasmania, but I expect the situation to be similar but less extreme. The energy company just can't offer a lot of money for solar exports because too many people are exporting solar power at the same time.

We also don't know how much energy he is using at night. If he's using multiple megawatts overnight and exporting megawatts during the day, then his property is destabilising the grid by drawing power when supply is low, and sending power when supply is already high.

Alternatively (or additionally), the energy provider could be incompetent or trying to make as much profit as possible, but we can't know without details.

I suspect that installing a large bank of batteries on site would fix these problems, but such a battery would be quite expensive.